I/Q MIMO detection for single antenna interference cancellation

ABSTRACT

An I/Q MIMO detection framework is a practical means to realize interference cancellation (IC) gains when GMSK, 8PSK signals interfere with each other in synchronous GSM/EDGE networks, thereby providing coverage, capacity, and throughput gain. Further, the presented algorithm applies to a high data rate system concept, in which multiple signals are transmitted from the base station (BTS) through multiple antennas.

TECHNICAL FIELD

The field of the invention is that of processing interfering RF signalsin a system having two or more signals that interfere with one another,in particular interference cancellation.

The present invention applies to Enhanced Data Rates for a GSM Evolution(EDGE) system in which two different modulation formats are used namelybinary Gaussian Minimum Shift Keying (GMSK) and 8 level Phase ShiftKeying (8PSK).

BACKGROUND OF THE INVENTION

As more signals are sent within a fixed amount of RF spectrum, there aremore occasions when signals interfere with another signal that isintentionally transmitted along the same channel, rather than beingrandom noise. When frequency spectrum is available on a limited basis asin cellular or PCS systems, the same frequency is reused ingeographically distinct regions (or cells) to maximize the spectrumefficiency. The overall system capacity is generally limited by theinterference caused by the reused frequencies.

Interference cancellation (IC) is traditionally achieved by the use ofmultiple antennas at the receiver terminal. However addition of antennasat the receiver significantly adds to the receiver cost. On the otherhand IC using a single antenna is an attractive way to increase systemcapacity since it eliminates the need for additional RF hardware costsince the algorithm can be implemented digitally in base band.

The recently discovered single antenna interference cancellation (SAIC)algorithms are specifically tailored for GMSK signal detection in thepresence of GMSK interferers. The ICUPC 1998 paper “CochannelInterference Cancellation within current GSM Standard” written by Triguiand Slock exploits the special properties of GMSK modulation for SAIC.

A number of other SAIC approaches have also been proposed in theliterature. Examples include: Ottersen, Kristensson, Astely, “Areceiver”, International Publication Number WO 01/93439; Arslan,Khayrallah, “Method and Apparatus for Canceling Co-Channel Interferencein a Receiving System Using Spatio-Temporal Whitening” InternationalPublication Number WO 03/030478 A1; Meyer, Schober, Gerstacker, “Methodfor Interference Suppression for TDMA- and/or FDMA Transmission”, filedDec. 19, 2001. Also of interest are B. Picinbono and P. Chevalier,“Widely Linear Estimation with Complex Data,” IEEE Trans. On. SignalProc, vol. 43, pp. 2030-2033, Aug, 1995; W. H. Gerstacker et al,“Equalization with Widely Linear Filtering,” ISIT2001; W. A. Gardner, S.V. Schell, “GMSK Signal Processors For Improved Communications Capacityand Quality, U.S. Pat. No. 5,848,105, Dec. 8, 1998;

The above-mentioned prior art is relevant for SAIC for GMSK signals orany other real modulation signals. However the literature has not dealtwith IC techniques involving both real and complex modulation alphabetssuch as GMSK and 8PSK signals, which are encountered in GSM/EDGEsystems. If SAIC gains are to be maximized in EDGE deployments it isnecessary to develop a mobile receiver that has interferencecancellation capability irrespective of the interference modulationtype.

IC methods are generally categorized into two classes namely blind IC,and Joint detection (JD). By “blind”, we mean that the channelparameters of the interfering signal are not known at the receiver andthat the interfering signal is not detected together with the desiredsignal as in JD. The paper titled “The Finite-Length Multi-InputMulti-Output MMSE-DFE written by Al-Dhahir and Sayed may be a usefulapproach for JD, though it does not handle GMSK-8PSK IC. Significantimprovement would be required to extend this technique to the GMSK-8PSKIC problem. So far no prior art is reported on IC involving 8PSK andGMSK signals.

The art would benefit from a system and method that is able to suppressinterference between 8PSK and GMSK signals.

SUMMARY OF THE INVENTION

The invention relates to a method for using interference cancellationwith various combinations of signals; e.g. GMSK and 8PSK in variouscombinations.

A feature of the invention is the detection of real and imaginary partsof an incoming set of signals that include at least one complex signal.

A feature of the invention is the rotation of the incoming complexsignal, if necessary (as in the case of GMSK) using parameters suppliedby previous estimations or by a base station so that the imaginarycomponent of the GMSK signal is eliminated.

Another feature of the invention is using an MIMO process on at leastthree input signals: the real GMSK signal and the real and imaginarycomponents of the 8PSK signal.

Another feature of the invention is a high data rate system in whichdeliberate interference is created by transmitting multiple signals fromthe same base station through spatially separated antennas. At thereceiver, signal separation is performed through interferencecancellation, without having multiple receive antennas.

For instance, the peak data rates for GPRS can be improved by a factorof 2 by transmitting two GMSK signals, and EDGE peak data rates can beimproved by 4/3 or 2 by transmitting GMSK-8PSK or 8PSK-8PSK signalssimultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a system employing the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a simplified block diagram of a portion of atelecommunications system in which base station 10 communicates withthree or more mobile stations 100, 200 and 300. Station 10 is connectedto a network 20, which may be a switched telephone (voice or data)network having as input voice handsets 22 and/or data terminals 24.

Mobile stations 100-300 have single or multiple antennas 112, 212 and312, respectively and communicate with the base station over channels110, 210 and 310. Illustratively, base station 10 has two or moreantennas 12 and 14. Base station 10 is capable of transmitting GMSKand/or 8PSK signals. Within base station 10, RF unit 16 handles the RF(and IF) signals, while processor unit 18 handles manipulation of thebaseband signals. Counterpart units 116, 216 and 316 for RF and 118, 218and 318 for baseband are located within the mobile stations 100-300.

The invention exploits the special properties of GMSK/BPSK signaling forimproved signal detection when GMSK/BPSK and 8PSK signals interfere witheach other. Unlike conventional detection methods, the invention relieson novel detection methods that detect the real (I) and imaginary (Q)parts of a combination of complex and real modulation alphabets forimproved signal processing.

We adopt the following notation throughout. The desired modulation typeis mentioned first, followed by the dominant interferer modulation typee.g in station 100, the signals are GMSK-8PSK; in station 200, thesignals are 8PSK-GMSK; and in station 300 the signals are 8PSK-8PSK. Thereceiver processing assumes a linearized GMSK signal model as specifiedin the papers by Laurent, “Exact and Approximate Construction of DigitalPhase Modulations by superposition of Amplitude Modulated Pulses (AMP)and Kaleh, “Simple Coherent Receivers for Partial Response ContinuousPhase Modulation”.

In an illustrative example, station 10 is transmitting to mobile unit100 and to mobile unit 200 using 8PSK and/or GMSK on the same frequencyband for both transmissions, so that each mobile unit will haveinterference. The type and significance of the interference will vary.

In the following discussion, the channel parameters h are assumed to beknown. When the interfering signal comes from the same base station asthe data, the base station can transmit to each mobile unit the relevantparameters of the interfering channel, thereby reducing the time spentby the mobile unit in estimating those parameters. When the interferingsignal comes from a different base station, the mobile unit will have toperform a conventional estimation process.

In a first example, the base station transmits data on the same channelin both GMSK and 8PSK formats to mobile station 100. Station 100 usestechniques according to the invention to detect the data in bothformats, thus increasing the bandwidth.

In a second example, the base station transmits two different signals(GMSK or 8PSK) using two antennas to two mobile units and cochannelinterference (8PSK or GMSK) comes from the same base station.

In a third example, the base station transmits a signal (GMSK or 8PSK)to a mobile unit and (8PSK or GMSK) cochannel interference comes from adifferent base station.

After converting from RF to baseband, a linearized GMSK signalrepresentation for simplified receiver processing is used to de-rotatethe received signal, which is a sum of one GMSK and one 8PSK signal,with a factor exp (−jkπ/2) (where k is the symbol time index), such thatall the component GMSK signals will be forced to be binary modulated.There are three data streams—a real-only stream from the GMSK data and areal and imaginary data streams from the 8PSK data.

This disclosure is directed at single antenna reception and jointdetection of at least two signals having same or different modulationsize for e.g., GMSK-GMSK, GMSK-8PSK, 8PSK-GMSK and 8PSK-8PSK scenariosor detection of a single 8PSK signal in the I/Q domain with additionalI/Q whitening capability. Although we are primarily interested in asingle receiver antenna, we present the algorithm for the general caseof N receiver antennas. Further we assume that the received signalcomprises M, GMSK co-channel signals and M₂ 8PSK signals and an additivenoise component, which may include the sum of residual co-channel oradjacent channel interfering signals and thermal noise. Then the complexbase band signal at the kth sampling instant can be represented as:$\begin{matrix}{{r_{k,q} = {{\sum\limits_{{i\quad 1} = 1}^{M_{1}}{\sum\limits_{m = 0}^{L}{h_{m}^{({i_{1},q})}a_{({{k - m},i_{1}})}{\mathbb{e}}^{{j\varphi}_{k - m}}}}} + {\sum\limits_{{i\quad 2} = 1}^{M_{2}}{\sum\limits_{m = 0}^{L}{h_{m}^{({i_{2},q})}b_{({{k - m},i_{2}})}{\mathbb{e}}^{{j\theta}_{k - m}}}}} + n_{k}^{q}}},{q = 1},\ldots\quad,{{N\quad S\quad{where}\quad\phi_{k}} = \frac{\pi\quad k}{2}},{\theta_{k} = \frac{3\pi\quad k}{8}}} & (1)\end{matrix}$are the modulation dependent constellation rotation factors as definedin the GSM/EDGE standard. For each symbol index k, the receiver collectsNS samples corresponding to an over-sampling factor of S at in case of Nreceiver antennas. Further h_(m) ^((i) ¹ ^(,q)) and h_(m) ^((i) ² ^(,q))denote the channel coefficients for mth tap, at the qth over sampledobservation, corresponding to i₁th binary symbol source a_(k-m,i) ₁ ,and i₂ 8PSK complex symbol source b_(k-m,i) ₂ respectively. Further weassume that the channel length is equal to L+1 for all signals.

When the data are contained in one format, then one sum in the precedingequation is the data and the other sum is the interfering signal to besubtracted. According to the embodiment illustrated, when the data arecontained in two formats (GMSK and 8PSK), the interfering signals are inthe n_(i); i.e. this example is not directed at the case when the dataare GMSK and 8PSK and there is significant interference.

Those skilled in the art will be able to generalize the examplepresented to handle interference by adding sums to equation 1 withchannel coefficients that represent the interfering channel.

The base band received signal, which is a sum of at least one GMSK or atleast one 8PSK signal, is first de-rotated with a factor e^(−jφ) ^(k)such that all the component GMSK signals are forced to be binarymodulated. The de rotated base band signal can be represented as$\begin{matrix}{{{\mathbb{e}}^{- {j\varphi}_{k}}r_{k,q}} = {{\sum\limits_{{i\quad 1} = 1}^{M_{1}}{\sum\limits_{m = 0}^{L}{{\overset{\sim}{h}}_{m}^{({i_{1},q})}a_{({{k - m},i_{1}})}}}} + {\sum\limits_{{i\quad 2} = 1}^{M_{2}}{\sum\limits_{m = 0}^{L}{{\overset{\sim}{h}}_{m}^{({i_{2},q})}{\overset{\sim}{b}}_{({{k - m},i_{2}})}}}} + {\overset{\sim}{n}}_{k}^{q}}} & (2)\end{matrix}$where the de-rotated quantities are denoted by the tilde symbol. Since8PSK is a complex modulation alphabet, multiplication with a complexde-rotation factor yields a constellation rotated 8PSK modulation.

After de-rotation, we split the real (I) and imaginary (Q) parts of thede-rotated GMSK-8PSK composite signal and represent in column vectorformat as: $\begin{matrix}{{y_{k,q} = {{\sum\limits_{{i\quad 1} = 1}^{M_{1}}{\sum\limits_{m = 0}^{L}{H_{a,m}^{({i_{1},q})}a_{({{k - m},i_{1}})}{\mathbb{e}}^{{j\phi}_{k - m}}}}} + {\sum\limits_{{i\quad 2} = 1}^{M_{2}}{\sum\limits_{m = 0}^{L}{H_{c,m}^{({i_{2},q})}c_{({{k - m},i_{2}})}{\mathbb{e}}^{{j\theta}_{k - m}}}}} + {\hat{n}}_{k}^{q}}}{{{where}\quad y_{k,q}} = \begin{pmatrix}{{Re}\lbrack {{\mathbb{e}}^{- {j\phi}_{k}}r_{k,q}} \rbrack} \\{{Im}\lbrack {{\mathbb{e}}^{- {j\phi}_{k}}r_{k,q}} \rbrack}\end{pmatrix}}} & (3)\end{matrix}$is the I-Q received samples in stacked up in column format,$H_{a,m}^{i_{1},q} = \begin{pmatrix}{{Re}\lbrack {\overset{\sim}{h}}_{m}^{i_{1},q} \rbrack} \\{{Im}\lbrack {\overset{\sim}{h}}_{m}^{i_{1},q} \rbrack}\end{pmatrix}$is the I-Q parts of GMSK channel stacked up in column format,$c_{{k - m},i_{2}} = \begin{pmatrix}{{Re}\lbrack {\overset{\sim}{b}}_{k - m}^{i_{2}} \rbrack} \\{{Im}\lbrack {\overset{\sim}{b}}_{k - m}^{i_{2}} \rbrack}\end{pmatrix}$is the column vector filled with I-Q parts of 8PSK symbol, and$H_{c,m}^{i_{2},q} = \begin{pmatrix}{{Re}\lbrack {\overset{\sim}{h}}_{m}^{i_{2},q} \rbrack} & {- {{Im}\lbrack {\overset{\sim}{h}}_{m}^{i_{2},q} \rbrack}} \\{{Im}\lbrack {\overset{\sim}{h}}_{m}^{i_{2},q} \rbrack} & {{Re}\lbrack {\overset{\sim}{h}}_{m}^{i_{2},q} \rbrack}\end{pmatrix}$is the corresponding 8PSK I-Q matrix channel, and${\hat{n}}_{k}^{q} = \begin{pmatrix}{{Re}\lbrack {\overset{\sim}{n}}_{k}^{q} \rbrack} \\{{Im}\lbrack {\overset{\sim}{n}}_{k}^{q} \rbrack}\end{pmatrix}$is the residual noise vector after I-Q split.

The 8PSK I-Q matrix channel H_(c, m)^(i₂, q)is orthogonal due to the inherent I-Q orthogonality.

Note that after de-rotation and I-Q split, we have three data modulationformats—binary data streams from GMSK sources and real and imaginarydata streams from the 8PSK sources.

Further y_(k,q) is represented in compact matrix form as:$\begin{matrix}{y_{k,q} = {{\sum\limits_{m = 0}^{L}{H_{m}^{q}d_{k - m}}} + {\hat{n}}_{k}^{q}}} & (4)\end{matrix}$in which we further stacked the I-Q parts of GMSK and 8PSK channel anddata matrices in matrix format as:H_(m)^(q) = [H_(a, m)^(1, q)  H_(c, m)^(1, q)  ⋯  H_(a, m)^(M₁, q)  H_(c, m)^(M₂, q)]  andd_(k-m)=[a_((k-m,1)) c_(k-m,1) ^(T) . . . a_((k-m,M) ₁ ₎ c_(k-m,M) ₂^(T)]^(T) is a column vector filled with I-Q parts of GMSK and 8PSKsymbols. Note that the superscript symbol T denotes a matrix transposeoperation.

We further stack the over samples corresponding to kth sample from allreceiver antennas in column format as:

-   -   y_(k)=[y_(k,1) ^(T) . . . y_(k,q) ^(T) . . . y_(k,NS) ^(T)]^(T)

Then we get the following compact signal definition $\begin{matrix}{{y_{k} = {{\sum\limits_{m = 0}^{L}\quad{{\hat{H}}_{m}d_{k - m}}} + n_{k}}}{{{i.\quad{where}}\quad{\hat{H}}_{m}} = {{\begin{bmatrix}H_{m}^{1} \\\vdots \\H_{m}^{NS}\end{bmatrix}\quad{and}\quad n_{k}} = \begin{bmatrix}n_{k}^{1} \\\vdots \\n_{k}^{NS}\end{bmatrix}}}} & (5)\end{matrix}$We then filter the received vector y_(k) with a set of feed forwardweights w such that the filtered signal has an impulse response withmost of the energy concentrated in the first few taps. This type offilter is also referred to as a channel-shortening filter in theliterature. The weights are chosen to minimize the error term defined ase_(k)=w^(T)y_(k+L) _(f) _(:k)−Bd_(k:k-L)

-   -   where B denotes the I-Q MIMO feedback filter.

We use the notation where y_(k+L) _(f) _(:k) is a vector that containsthe blocks y_(k+L) _(f) , . . . y_(k), where each block is a vector ofsize 2NS×1. Note that we have assumed a finite length feed forwardfilter of length L_(f). The feed forward filtered received signalx_(k)=w^(T)y_(k+L) _(f) _(:k) has the following signal structure$x_{k} = {{\sum\limits_{l = 0}^{L}\quad{B_{l}d_{k - l}}} + e_{k}}$

We further define the error auto correlation matrix asR_(ee)≅E[e_(k)e_(k) ^(T)]

We then optimize the filter coefficients according to the minimum meansquare error (MMSE) criterion by minimizing the trace of the errorautocorrelation matrix R_(ee)$w^{opt},{B^{opt} = {\arg\quad{\min\limits_{w,B}{{Trace}( R_{ee} )}}}}$such that first tap of the feedback filter matrix is constrained to beB₀=I or a lower triangular matrix.

The pre filtering step thus allows a decision feedback equalizer (DFE)or a reduced state sequence estimation (RSSE) algorithm can be applied.

A subsequent reduced state soft output sequence estimation algorithm(using one of MAP/Max-Log-MAP/SOVA algorithms) jointly detects the I/Qsymbol streams using the shortened impulse response B^(opt).Furthermore, the constellation rotated 8PSK symbol set will be used inthe equalizer branch metric computations. The branch metric is given by$\begin{matrix}{{d^{2}(k)} = {( {x_{k} - d_{k} - {\sum\limits_{l = 1}^{L}\quad{B_{l}{\hat{d}}_{k - l}}}} )^{T}{R_{ee}^{- 1}( {x_{k} - d_{k} - {\sum\limits_{l = 1}^{L}\quad{B_{l}{\hat{d}}_{k - l}}}} )}}} & (6)\end{matrix}$

-   -   where {circumflex over (d)} indicates the state dependent path        history vector in a joint RSSE algorithm. We note the difference        between the novel branch metric above made up with I-Q parts of        the composite signals, and a conventional branch metric defined        using complex quantities.

The result of the foregoing is that the desired signal emerges from theMIMO process, with the interfering signal removed as part of thesequence estimation process. A similar procedure is followed in mobilestations 100 and 200.

The I/Q MIMO MMSE framework described above includes the followingscenarios as special cases.

By setting M1=0 and M2=1, the invention can be configured as an 8PSKblind I/Q interference suppression receiver when a GMSK interferer ispresent.

The invention can be configured as GMSK-8PSK or 8PSK-GMSK I/Q MIMO MMSEjoint detection receiver if we let M1=1 and M2=1

The invention can be configured as 8PSK-8PSK I/Q MIMO MMSE receiver ifwe let M1=0 and M2=2. In this mode the receiver jointly detects two 8PSKsignals and rejects any residual GMSK interference through I-Qwhitening.

The invention can be configured as GMSK-GMSK I/Q MIMO MMSE receiver ifwe let M1=2 and M2=0. In this mode the receiver jointly detects two GMSKsignals and rejects any residual GMSK interference through I-Qwhitening.

Many other possibilities include for instance joint detection of 3 ormore signals (for example 2 GMSK and one 8PSK) in I-Q domain.

In a practical implementation, the receiver can be made to switchbetween the above realizations by examining the desired and interferingsignal channel estimates. Those skilled in the art will readily be ableto set up criteria for switching, based on their needs.

Joint Channel Estimation

In an optional version of a system according to the invention, areceiver sequentially estimates the desired and dominant interferingtransmissions and applies the cancellation process described above.

In this section we outline a joint channel estimation method thatestimates the desired and dominant interferer signal channel impulseresponses. The channel estimation method blindly (without a prioriknowledge) identifies the dominant interferer modulation type (GMSK or8PSK) and its training sequence (TRS) number during the estimationprocess. The modulation identification is done by exploiting thee^(jπk/2), e^(j3πk/8) constellation rotations associated with GMSK and8PSK modulations respectively, where a TRS identification is madepossible by formulating a maximal likelihood metric (or a simplecorrelation or least squares or LMMSE metric) over all possible desiredand interference training sequence pairs.

In one embodiment of the invention, the receiver may first identify thedesired signal modulation type and training sequence number by searchingthrough the known relatively small number of training sequences. Next,the receiver analyzes the residual signals to identify the type ofinterference that is dominant.

In more detail, the estimation method consists of the following steps:

First, de-rotate the received signal by e^(jπk/2) as above. Thede-rotation process forces the GMSK component signals to be binary.

Then solve for the channel estimate using one of maximal likelihood(ML), or least minimum mean square estimation (LMMSE) or anotherconvenient method of optimization for all possible desired andinterference training pairs. Solve for the channel estimate {tilde over(H)}_(l) using the following ML metric $\begin{matrix}{\min\limits_{{\hat{H}}_{l}}{{y_{k} - {\sum\limits_{m = 0}^{L}\quad{{\hat{H}}_{l}d_{k - m}}}}}^{2}} & (7)\end{matrix}$

In another embodiment of the invention, a reduced complexityimplementation may be devised such that the interfering modulation typeand TRS number are estimated sequentially, then a final ML joint channelestimate can be made once all modulation types and TRS numbers areestimated.

Implementation Alternatives

The invention provides many implementation alternatives:

The preceding discussion has implicitly assumed that the interferingsignal is unwanted. In one embodiment of the invention, the base stationtransmits two signals on the same channel, with both the signals beingpart of the message. In that case, both signals are important and needto be detected accurately.

The base station transmits the signals on two (or more) differentspatially separated antennas. The receiving station has only a singleantenna and applies one of the techniques described above to separatethe two signal streams and discard interference between the streams.

When both the signals are GMSK, the data rate can be doubled. When onesignal is GMSK and the other is 8PSK, the data rate can be improved by afactor of 4/3.

If 8PSK is the desired signal and GMSK is the source of interference,the invention can be configured as an 8PSK blind I/Q whitener thatwhitens the GMSK signal as colored noise in I/Q space.

Alternatively, if 8PSK is the desired signal and GMSK is the source ofinterference, the invention can jointly detect desired and interferingsignals in I/Q space. Similarly, if GMSK is the desired signal and 8PSKis treated as CCl, the same algorithm can be used for interferencecancellation (IC). If 8PSK is the desired signal and the CCl comprises adominant 8PSK and a residual GMSK interferer, the algorithm can jointlydetect two 8PSK signals and also whitens the GMSK interference in I/Qspace

For example, an alternate version of the invention includes a subsystemfor detecting whether the transmission-receiver system is in a firsttransmission mode in which the interfering signal is to be discarded(i.e. the second signal is directed at another mobile station, etc.) oris in a second transmission mode in which the first signal and thesecond signal are both to be processed as data (i.e. the high data ratemodes discussed above); and

-   -   processing the second signal accordingly (e.g. discarding or        saving it).

A transmission system may be set up with a convention such that thedefault primary format is GSM and a secondary format of e.g. 8PSKindicates that the high data rate mode is on, so that the second signalis to be saved and combined with the first signal; while a secondarysignal having another format is to be discarded.

Although the invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate thatother embodiments may be constructed within the spirit and scope of thefollowing claims.

1. A method of receiving a wireless communication having at least twosignals selected from the group comprising GMSK signals and 8PSK signals(with interference between the signals), comprising the steps of:Receiving the incoming signals; Rotating the raw incoming signals incomplex space with a factor such that the GMSK signal is binarymodulated; Detecting the rotated signal as two signal streams composedof real (I) and imaginary (Q) signals in a detector; Processing the Iand Q signal streams with a MIMO filter; and Processing the output ofthe MIMO filter with a joint reduced state sequence estimator based onthe filtered channel impulse response
 2. A method according to claim 1,in which the desired signal is an 8PSK signal; a set of 8PSK trainingsymbols are rotated by e^(j(θk-φk)); and channel estimation parametersare found by one of a maximal likelihood (ML), or a least minimum meansquare error estimation procedure.
 3. A method according to claim 2, inwhich the interfering signal is an 8PSK signal.
 4. A method according toclaim 2, in which the interfering signal is a GMSK signal.
 5. A methodaccording to claim 1, in which the interfering signal is an 8PSK signal;a set of interfering 8PSK training symbols are rotated by e^(j(θk-φk));and channel estimation parameters are found by one of a least squares ora least minimum mean square error estimation procedure.
 6. A methodaccording to claim 5, in which the desired signal is an 8PSK signal. 7.A method according to claim 5, in which the desired signal is a GMSKsignal.
 8. A method of sending a wireless communication comprising thesteps of: transmitting on a channel from two or more spatially separatedantennas at least two signals selected from the group comprising GMSKsignals and 8PSK signals (with interference between the signals),Receiving the incoming signals; Rotating the raw incoming signals incomplex space with a factor such that the GMSK signal is binarymodulated; Detecting the rotated signal as two signal streams composedof real (I) and imaginary (Q) signals in a detector; Processing the Iand Q signal streams with a MIMO filter; and Processing the output ofthe MIMO filter with a joint reduced state sequence estimator based onthe filtered channel impulse response
 9. A method according to claim 8,in which a first signal is an 8PSK signal; a set of 8PSK trainingsymbols are rotated by e^(j(θk-φk)); and channel estimation parametersare found by one of a least squares or a least minimum mean square errorestimation procedure.
 10. A method according to claim 9, in which asecond signal is an 8PSK signal.
 11. A method according to claim 9, inwhich a second signal is a GMSK signal.
 12. A wireless transmissionsystem comprising: At least one base station having at least twospatially separated antennas and at least one RF unit for transmittingone of a GMSK and an 8PSK transmission signal along each of said twospatially separated antennas; At least one receiving station, having asingle antenna, for communicating with said base station; in which Saidreceiving station has processor means for applying interferencecancellation to a composite input signal comprising a combination of afirst signal and a second signal interfering with said first signal,thereby reducing interference between said first signal and said secondsignal.
 13. A system according to claim 12, in which said base stationtransmits two transmission signals on the same channel.
 14. A systemaccording to claim 13, in which said two transmissions signals comprisetwo GMSK signals.
 15. A system according to claim 13, in which said twotransmissions signals comprise two 8PSK signals.
 16. A system accordingto claim 13, in which said two transmissions signals comprise one 8PSKsignal and one GMSK signal.
 17. A system according to claim 12, in whichsaid receiving station comprises means for evaluating the modulationtype of an interfering signal and for estimating channel parameters ofsaid interfering signal.
 18. A system according to claim 17, in whichsaid channel parameters of said interfering signal are estimated bycalculating channel parameters for all combinations of a desired signaland of said interfering signal and selecting the channel parameters thatmeet a criterion.
 19. A system according to claim 17, further comprisingmeans for: detecting whether said system is in a first transmission modein which said interfering signal is to be discarded or is in a secondtransmission mode in which said first signal and said second signal areboth to be processed as data; and processing said second signal inaccordance with said transmission mode.
 20. A method of receiving awireless communication comprising M1 GMSK signals, M2 8PSK signals andan additive noise component, comprising the steps of: Receiving theincoming signals; Rotating the raw incoming signals in complex I/Q spacewith a factor such that the GMSK signal is binary modulated; Detectingthe rotated signal as two signal streams composed of real (I) andimaginary (Q) signals in a detector; Processing the I and Q signalstreams with a MIMO filter; and Processing the output of the MIMO filterwith a joint reduced state sequence estimator based on the filteredchannel impulse response
 21. A method according to claim 20, in whichM1=0 and M2=1 and the step of processing comprises blind interferencesuppression of a GMSK interferer.
 22. A method according to claim 20, inwhich M1=1 and M2=1 and the step of processing comprises joint detectionof one GMSK and one 8PSK signal.
 23. A method according to claim 20, inwhich M1=0 and M2=2 and the step of processing comprises joint detectionof two 8PSK signals with suppression of GMSK interference through I-Qwhitening.
 24. A method according to claim 20, in which M1=2 and M2=0and the step of processing comprises joint detection of two GMSK signalswith suppression of GMSK interference through I-Q whitening.